This invention relates to a rotational drive control device for a variable speed drive motor arranged in a rotational drive system of any concerned equipment in a factory or the like, and more particularly to a rotational drive control device for a variable speed drive motor which is adapted to carry out rotational drive control of the variable speed drive motor according to a radio communication system.
Conventionally, a variable speed drive control system (hereinafter referred to as "VSD control system") has been generally known to those skilled in the art in connection with rotational drive control for a variable speed drive motor and, in particular, rotational speed control therefor.
Such a VSD control system for a variable speed drive motor permits rotational drive control of the variable speed drive motor to be highly smoothly executed over a wide rotational speed range extending from a low rotational speed to a high rotational speed, to thereby significantly reduce power consumption of the motor. Thus, the system tends to be widely applied to rotational drive speed control for a variable speed drive motor constituting a rotational drive system of any desired equipment such as an FA device, a belt conveyor, a crane, a water cooler, a pump or the like in a concerned factory or the like.
Rotational speed control of the variable speed drive motor utilizing the VSD control system is carried out, as a principle, by rectifying and smoothing commercial AC power for rotational drive of a three-phase induction motor used as the variable speed drive motor to be controlled to convert it into DC power and converting the converted DC power into AC power of a frequency required for rotational drive control of the variable speed drive motor again, to there by obtain drive power.
In the stage of converting the DC power to the AC power again, an electrical circuit is used to obtain AC power of any desired frequency, so that it is possible to readily attain smooth rotational drive control of the variable speed drive motor over a wide rotational speed range extending from a lower rotational speed to a high rotational speed as described above.
The VSD control system is used in various manners extending from rotational drive control carried out while individually controlling variable speed drive motors to that carried out while centralizedly controlling a plurality of variable speed drive motors.
For example, a control signal generated from a detection sensor for temperature monitor control or the like may be input to the variable speed drive motor in conformity to a control signal of a rotational speed input thereto, to thereby accomplish whole process control for a rotational drive system of any desired equipment.
In such applications of the VSD control system, the control may be carried out through a control panel equipped in an equipment which is desired to be subject to control. In this instance, it is required to carry out centralized control, remote control or the like, therefore, the equipment generally includes input terminals for receiving control signals from an exterior thereof. Thus, the control is carried out depending on input of each of the external control signals thereto. For this purpose, for example, a voltage signal of about 0 to 10 V or a current signal of 4 to 20 mA is generally used as an analog signal for the rotational speed control.
When centralized control of the variable speed drive motors of the rotational drive system is to be carried out; it is required that a signal transmission cable is laid between a centralized control center and each of equipments of a VSD system to be controlled for remote control therebetween, so that a VSD control signal, as well as a sensor control signal or the like as required is transmitted according to a wire communication system.
However, in control of a rotational drive speed of the variable speed drive motor carried out using the VSD control system as described above, the control signal is transmitted according to the wire communication system. Unfortunately, this leads to the following disadvantages.
One of the disadvantages is that laying of the signal transmission cable between the centralized control center and each of equipments to which control of the VSD control system is to be applied causes a significant increase in cost.
Another disadvantage is that an increase in cost due to laying the signal transmission cable between the centralized control system and the equipment imposes restrictions on and/or deteriorates flexibilities such as arrangement of the equipment, lay-out thereof, relocation thereof, and the like.
A further disadvantage is that when laying of the signal transmission cable is impossible from positional and/or physical points of view, application of the VSD control system is substantially restricted.
Still another disadvantage is that when the equipment which is to be subject to control according to the VSD control system is located far away from a control section thereof, it is highly difficult and troublesome to carry out maintenance thereof.
It would be considered that a radio communication system is employed for transmission of the signal in order to eliminate the above-described disadvantages. Unfortunately, a radio system by means of a conventional regular communication system causes an environment surrounding the equipment to which control according to the VSD control system is applied to be ruined due to generation of noise from the equipment, resulting in being substantially impossible to be realized.